Hey SFC H, first off, thank you for your incredible 24 years of service, Desert Storm, OIF, the whole nine yards. That's a serious commitment.
Regarding your MEB/VA strategy: I strongly recommend following your Military Service Coordinator's advice: sign the 21-4138 and do NOT file new claims right now. You already have a robust 90% rating. Introducing new claims (Hypertension, ED, etc.) into the MEB/IDES process complicates things significantly and, more importantly, can trigger a full review and new C&P exams for all your existing ratings. The risk of a reduction, though small, is not worth the potential speed bump.
Your best move is to let the MEB focus only on the "unfit" conditions (PTSD and Knees) to finalize your separation and benefits. Once you are officially retired/separated, immediately file a Notice of Intent to File (NOI) for the other conditions. You can then file the ED as a secondary claim linked to your PTSD medication, and the knee increase after your surgery. This strategic timing protects your current 90% rating while ensuring you get compensated for everything you deserve later. Good luck with the process, brother.